1. Field of the Invention
The present invention relates to a thermal head controller for controlling a thermal head that easily forms an arbitrary-image print face on a roller stamp material.
2. Description of the Related Art
In Japanese Unexamined Patent Application No. 3-96383, there have been disclosed as conventional methods for producing a print face made of sponge rubber having continuous bubbles, the following techniques for selectively clogging continuous pores:
(1) Performing the screen printing of a clogging adhesive; PA1 (2) Spraying a clogging adhesive on a masked area before removing the mask; PA1 (3) Bonding a thermosensitive pourous film to cause clogging before using a thermal head or flash heat to make pores; PA1 (4) Using a thermal head or flash heat to transfer a trans-thermo film to cause clogging; PA1 (5) Using a thermal head to directly heat and melt a surface to cause clogging; and PA1 (6) Emitting light onto photocurable resin to cause clogging, whereby forming the stamp print face of a plane stamp. PA1 pattern data P2={P2.sub.1, P2.sub.2, P2.sub.3, P2.sub.4, P2.sub.5 } PA1 pattern data P3={P3.sub.1, P3.sub.2, P3.sub.3, P3.sub.4, P3.sub.5 } PA1 pattern data P4={P4.sub.1, P4.sub.2, P4.sub.3, P4.sub.4, P4.sub.5 } PA1 pattern data P5={P5.sub.1, P5.sub.2, P5.sub.3, P5.sub.4, P5.sub.5 } PA1 pattern data P6={P6.sub.1, P6.sub.2, P6.sub.3, P6.sub.4, P6.sub.5 } PA1 pattern data P7={P7.sub.1, P7.sub.2, P7.sub.3, P7.sub.4, P7.sub.5 }
In Japanese Unexamined Patent Application No. 6-155698, there has been disclosed a technique in which heat waves are selectively emitted to a polyolefin foam sheet surface having continuous bubbles to form the stamp print face of a plane stamp.
In Japanese Unexamined Patent Application No. 7-251558, there has been disclosed a method for producing the stamp print face of a plane stamp by compressing an elastic resin sheet in which stamp ink having continuous bubbles can be impregnated between a thermal head and a platen.
In fact, concerning the above-described methods, the advent of a polyethylene foam sheet made by Yamahachi Chemicals Co., Ltd. has realized a remarkable impregnated stamp that has never existed.
In the above-described formation of a stamp print face with a thermal head, a polyethylene foam sheet is deformed by its heat conduction. For example, in the case where the print pattern shown in FIG. 2A is printed on the polyethylene foam sheet by using the dots of the thermal head, it is ideal to obtain a stamp print face having the section shown in FIG. 2B. In FIGS. 2A and 2B, black circles indicate a print-dot pattern, and white circles indicate a non-print dot pattern.
However, an actually obtained stamp print face has the section shown in FIG. 9B. The section is formed by a phenomenon in which thermal energy from the dots of the thermal head diffuses to deform the non-print dots in region R1 shown in FIG. 9A.
As a result, in the section of the print face shown in FIG. 9B, although region R2 must be included in non-print area S, it is deformed due to the heat diffusion in the polyethylene foam sheet to form print area Q.
Accordingly, the polyethylene foam sheet has a disadvantage in which contraction due to the above-described deformation causes bubble clogging beyond a necessary range for the stamp print face. This causes a problem in which fine printed lines on the stamp print face are erased. When the thermal head uses the thermal energy from heating resistors to perform continuous printing, the thermal energy is accumulated to increase the temperature. In addition, in the heating resistors is left heating energy generated just before the continuous printing.
Therefore, non-print dots surrounded by pint dots are deformed by the above-described factors, and are clogged by bubbles in the polyethylene foam sheet. As a result, according to the above-described, conventional thermal head controller, the non-print dots around the print dots disadvantageously have a condition similar to the case where the printing by the thermal head is performed.
In other words, when the pattern shown in FIG. 5A is used to perform printing, the section of a print face on a polyethylene foam sheet taken on dotted line A-A' is formed such that the section of non-print dots R1, shown in FIG. 5B, becomes the section of region R1. The thermal head performs printing on the polyethylene foam sheet in the order of pattern data P1 to P7. Black circles indicate print dots, and while circles indicate non-print dots.
Pattern data P1 consists of a set of dot data {P1.sub.1, P1.sub.2, P1.sub.3, P1.sub.4, P1.sub.5 }. Similarly,
Region R1 shown in FIG. 5B is formed based on dot data P6.sub.3 corresponding to a non-print dot. In the pattern data, dot data P6.sub.3 is adjacent to dot data P5.sub.2, P5.sub.3, P5.sub.4, P6.sub.2, P6.sub.4, P7.sub.2, P7.sub.3 and P7.sub.4. Accordingly, region R1 corresponding to dot data P6.sub.3 is deformed to have the shape of region R2, due to heating energy accumulated in the thermal head, heating energy left in the heating resistors, and the diffusion of thermal energy in the polyethylene foam sheet.
Similarly, as described above, the polyethylene foam sheet has a defect in which contraction caused by the deformation generates bubble clogging beyond a necessary range for the stamp print face. This causes a problem in which fine lines on the stamp print face are erased.